Transesterification reactions between the polycarbonate and polyesters can occur during melt blending that result in the deterioration of rheological and physical properties and generation of gaseous by products, such as carbon dioxide. In addition, melt blending of polycarbonate and polyesters can result in an unacceptable increase in color despite the fact that the components themselves are initially colorless. It is generally accepted that both transesterification and color generation during melt blending are promoted by metallic catalyst residues from the polycondensation processes used to manufacture polyesters. These problems are overcome in practice by addition of a stabilizer often referred to in the art as a catalyst deactivator or catalyst quencher that functions to deactivate the metallic catalyst residues. The use of phosphorus-containing compounds to deactivate metallic catalyst residues is disclosed in U.S. Pat. Nos. 4,532,290 and 4,401,804. Examples of phosphorus-containing compounds that are suitable as catalyst deactivators include bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite (Ultranox 626 available from GE Specialty Chemicals), distearyl pentaerythritol diphosphite (Weston 619 available from GE Specialty Chemicals), and bis(2,4-dicumylphenyl) pentaerythritol diphosphite (Doverphos 9228 available from Dover Chemical Qorporation). It is known that phosphorus containing compounds partially hydrolyze to generate acidic species over time and during extrusion processing. Hydrolysis is a prerequisite for effective catalyst deactivation (see for example, Polym. Eng. Sci. 29(18) 1226 (1989), Polym. Bull. 21 327 (1989), and J. Appl. Polym. Sci. 40 977 (1990)). Inorganic phosphite ester compounds such as metal salts of phosphite ester compounds may also be used as catalyst quenchers; however, they may impart haze or loss of clarity to the blends. Stabilization of polycarbonate-polyester blends using phosphorus-containing compounds is disclosed in U.S. Pat. Nos. 3,953,539, 4,088,709, 4,532,290, 4,981,898, 5,441,997, 5,907,026, and 6,221,556.
The detrimental effect of phosphorus-containing catalyst quenchers on the hydrolytic stability of polycarbonate and polycarbonate-polyester blends is disclosed in U.S. Pat. Nos. 4,456,717, 5,354,791, 5,744,526, 6,103,796, 4,393,158, and 6,107,375. Improved hydrolytic stability for polycarbonates stabilized with phosphorus-containing compounds and siloxanes containing oxetane groups are disclosed in U.S. Pat. No. 4,456,717. Improved hydrolytic stability for polycarbonates stabilized with phosphorus-containing compounds and an oligomer or polymer containing at least one pendant cyclic iminoether group per molecule is disclosed in U.S. Pat. No. 6,107,375. Improved hydrolytic stability for polycarbonates stabilized with phosphorus-containing compounds and an epoxy compound is disclosed in U.S. Pat. No. 4,393,158. Improved hydrolytic stability for polycarbonate-polyester blends stabilized with phosphorus-containing compounds and a polyester having epoxy functionality is disclosed in U.S. Pat. No. 5,354,791. Improved hydrolytic stability for polycarbonates stabilized with phosphorus-containing compounds and hexamethylenetetraamine is disclosed in U.S. Pat. No. 5,744,526. Specifically, U.S. Pat. No. 5,744,526 teaches the addition of the amine to stabilize the phosphite against hydrolysis and consequently improving the hydrolytic stability of the polycarbonate composition. Similarly, improved hydrolytic stability of certain phosphorus containing compounds by addition of a hindered amine light stabilizer (HALS) is disclosed in U.S. Pat. No. 6,103,796.
There is a need in the art for compounds that are useful in deactivating metal catalyst residues in polycarbonate, polyesters and polyester/polycarbonate blends without compromising the hydrolytic stability or weatherability of the polymer composition.